Book of 99

by Relax Gaming

Book of 99 is a 5-reel, 10 payline mythical-themed slot developed by Relax Gaming famed for one thing, and one thing only... An absolutely incredible 99% RTP! There truly aren't any slots out there that can hold a candle to this 2021 release when it comes to returns. Free spins with expanding symbols and a maximum win potential of 5,000x the player's stake makes this slot worth playing!

Slot information

RTP: 99.00%
Volatility: Medium
Max Payout: 5,000x stake
Reels: 5
Paylines: 10
Jackpot: No
Min Bet: 0.10
Max Bet: 100.00
Themes: Adventure, Mythical
Release Date: 2nd May 2021

Our rating

“ This mythical book slot might be a tad bland, but is worth playing for its RTP ”

3.4 out of 5

Win potential

Play Book of 99

Jump straight into the action and play Book of 99 now at the following fully licenced UK slot sites. These slot sites have been thoroughly audited and reviewed by the team here at Slot Gods to ensure they offer an exceptional user experience, are trustworthy, safe, secure, and boast the best selection of online slots in their portfolio including Book of 99...

Book of 99 Screenshots

Book of 99 Features

Free Spins

If players land 3 or more wild symbols (The Book of 99) then they'll automatically trigger the free spins bonus which sees them awarded with 10 spins. Ahead of this a special symbol is chosen beforehand to randomly expand every time it lands. 

The expanding symbol can expand to pay out on all 10 lines, according to the number of symbols landed and the corresponding pay table value. This symbol will pay out on each line even if the symbols are not connected from left to right.

Collected Wilds

Every time players land a wild symbol during base gameplay it will be added to a meter on top of the map of Ancient Greece to the left of the game reels. Once players have collected 99 wild symbols they'll automatically trigger the free spins bonus. 

The free spin bonus will be played with a bet size that accurate corresponds to the average bet size used whilst collecting all 99 of the wild symbols.

Book of 99 - Free Spins

Free Spins

Upon landing 3 or more Book of 99 wild symbols players will automatically trigger the free spins bonus, awarding them with 10 free spins with special expanding symbols.

Book of 99 - Collected Wilds

Collected Wilds

Players can trigger the free spins bonus by collecting 99 Book of 99 wild symbols during base gameplay. The bet size will correspond to the average bet size during the time it has taken to collect said symbols.

Play now

Book of 99 Review

WOW! Book of 99 is without a doubt the best online slot we've ever come across in terms of offering a mightily impressive return to player... As the name suggests this mythical-themed slot has a mindblowing RTP of 99%, which is absolutely unheard of in the world of iGaming. Props to Relax Gaming for being innovators, creating something slots fans have been pining after for some time.

This unique 5 reel, 10 payline slot offers players the chance to trigger 10 free spins with expanding symbols. These spins can be trigger by way of landing 3 wild symbols anywhere on the reels or by collecting 99 wild symbols and filling up a meter during base gameplay.


This slot takes inspiration from ancient Greece. The game's reels are set upon grand stone pillars with a map of Ancient Greece and Makedon (now known as Macedonia) is carved into the left-hand side. Upon the reels are symbols featuring characters from mythological tales, these include Lamia, a child-eating monster, a one-eyed Cylops, a mysterious female heroine and a dashing Greek hero. Low paying symbols are your standard 10, J, Q, K, A and 10. Book of 99's special wild symbol is the Book of 99 itself. 


Unlike most Relax Gaming slots, Book of 99 is actually incredibly straight-forward in terms of general gameplay! The only major mechanic of note is the wild collection meter that can be found to the left of the reels.

In terms of navigating Book of 99, everything is found along an action bar at the bottom of the game reels. From left-to-right there's a hamburger menu (which gives players access to game settings and the paytable), mute button, a stake selection tool, turbo spin, the spin button and an autoplay button (that allows players to set an infinite number of automated spins).

Win Potential

Of course, this first-of-its-kind slot has an incredibly inviting RTP of 99%, meaning for ever £100 you spin, you can expect to see £99 returned! Considering that the industry average RTP for most slots sits around 96%, how can we possibly turn out noses up at this medium volatility slot! The maximum win players can enjoy whilst playing Book of 99 is 5,000x their stake, which for a game with an RTP of 99% isn't at all bad 

Our Verdict

There's certainly no shortage of 'Book of' slots, that being said Relax Gaming's latest offering to this already saturated market is a welcome one! It might well be a bit of gimmick game, but you know what... We enjoyed it! The gameplay is simple and they've not done anything particularly special... But when you factor in the 99% RTP this game quickly becomes a must play. 

Sam Gascoyne
Reviewed by Sam Gascoyne Last updated on

A keen sports bettor, Sam took his first foray into the world of online slots when Bonanza Megaways caught his eye, he’s never looked back since! He joined the team in 2019 and has developed an encyclopedic knowledge of online slots, he isn’t afraid to voice his honest opinion when reviewing new games, even if it does ruffle a few feathers.

Learn more about Sam here

Play Book of 99

Play Book of 99 now at the following verified UK slots sites. These slot sites are fully licenced and have been thoroughly vetted and reviewed by us to ensure they offer a great user experience, are trustworthy, secure, and have a wide variety of the best online slots in their lobbies including Book of 99:-

Slots you may also like...

Enjoyed Book of 99? Here's a handful of similar slots we think you'll like too. These online slots have been chosen based on features and themes similar to Book of 99. You might also want to check out other Relax Gaming slots.